The questions are on the atmospheric pressure test. Take it under real conditions before reading the mark scheme.
Quick answer: Air is a mixture of gases, mainly 78 % nitrogen and 21 % oxygen, and it has mass: about 1.2 kg per cubic metre. This mark scheme gives the model answers and the marks for the 8 questions of the grade 7 science test on atmospheric pressure, from composition of air to unit of pressure, with the equivalent answers to accept.
Use these model answers with the marking notes. Give method marks when the substitution is correct even if the final number is wrong, and check that every pressure answer has the correct unit: Pa, kPa or hPa.
Level: Grade 7 science (Year 8 · Class 7) · Curriculum: MS-ESS2-5
Question 1 Composition of air (3 marks)
- Nitrogen.
- About 21 %.
- Argon or carbon dioxide (or water vapour).
Marking: 1 mark each.
Question 2 Evidence for mass (2 marks)
The inflated ball has a greater mass than the flat ball. The extra mass is the mass of the air added, so air has mass.Marking: 1 mark for the greater mass of the inflated ball, 1 mark for the conclusion that air has mass.
Question 3 Air in a hall (3 marks)
- V = 5.0 × 4.0 × 2.5 = 50 m³.
- m = ρ × V = 1.2 × 50 = 60 kg.
Marking: (a) 1 mark; (b) 1 mark for the substitution, 1 mark for the answer with unit.
Question 4 Pressure calculation (3 marks)
- p = F ÷ A = 480 ÷ 0.40 = 1200 Pa.
- 1200 ÷ 1000 = 1.2 kPa.
Marking: (a) 1 mark for the substitution, 1 mark for the answer with unit; (b) 1 mark.
Question 5 Reading a barometer (3 marks)
- 752 mm.
- A vacuum (no air).
- The pressure of the atmosphere pushing on the mercury in the dish.
Marking: 1 mark each part.
Question 6 Pressure on a mountain (3 marks)
- There is less air above a climber at the top, so the weight of the air column is smaller. The air is also less dense.
- The column becomes shorter.
Marking: (a) 1 mark for less air above, 1 mark for smaller weight or lower density; (b) 1 mark.
Question 7 Converting pressure (2 marks)
1020 × 100 = 102 000 Pa, and 102 000 ÷ 1000 = 102 kPa.Marking: 1 mark for pascals, 1 mark for kilopascals.
Question 8 Unit of pressure (1 mark)
1 Pa = 1 N/m² (one newton on one square metre).Marking: 1 mark.
